intro to met pt 2

Metabolic Pathways

Many biological reactions are endothermic, requiring energy input to drive them to completion.
Energy can be supplied in various ways, with a common method being the hydrolysis of Adenosine Triphosphate (ATP).

Structure of ATP:
- Composed of:
  - Adenine base
  - Ribose sugar ring
  - Three phosphate groups linked in a chain.
- High-energy molecule due to repulsion between negatively charged phosphate groups.
Hydrolysis of ATP:
- ATP can be hydrolyzed to two different molecules:
  - Adenosine Diphosphate (ADP): Removal of one terminal phosphate group.
    - Structure: Identical to ATP but with one less phosphate.
    - Free energy change: -30.5 kJ/mol.
  - Adenosine Monophosphate (AMP): Removal of two phosphate groups from ATP.
    - Results in Pyrophosphate (PPI) as other product.
    - Free energy change: -45.6 kJ/mol.
Equilibrium:
- Cells maintain an equilibrium ratio of ATP to ADP, typically around 500:1.
- Hydrolysis of ATP can significantly change the equilibrium constant for coupled reactions, by a factor of 10^8, allowing it to drive unfavorable reactions forward.

Cells must also balance ATP levels with reducing agents like NADH and NADPH.
Nicotinamide Adenine Dinucleotide (NAD):
- Common redox reagent in biological reactions, existing in oxidized and reduced forms.
- Structure: Two ribose rings linked by a phosphate group, with the oxidized nicotinamide ring being key in reactions.
- Reduction involves the addition of a hydride ion to the carbon at position four of the nicotinamide ring.
NAD vs. NADP:
- NADP has a phosphate group on the ribose ring, differentiating it from NAD.
- Enzymes in the cell selectively use NAD or NADP based on the presence of the phosphate group, allowing distinct control over oxidative and reducing reactions.

Understanding ATP hydrolysis and the roles of reducing agents like NAD and NADP is fundamental in comprehending cellular metabolism.